Conductivity cells and probes are a well recognized means for measuring the conductivity of electrolytes. Electrolytic conductance is the transport of electric charge under electric potential differences by particles of atomic or larger size. This phenomenon is distinguished from electronic or metallic conductance which is due to the movement of electrons. Electrolytic conductors may be solids, liquids or gases. Conductance is usually measured as the specific conductance, .kappa., which is the reciprocal of the resistance of a cube of material, 1 cm in each direction, placed between electrodes 1 cm.sup.2, on opposite sides of the cube. Conductances of solutions and solids are usually measured by the Kohlrausch method in which a Wheatstone bridge is employed. The conductance cell containing the electrolytic conductor between electrodes is placed is one arm of the bridge. By using an alternating current between the electrodes of the cell, the electrochemical reactions are reversed on the half cycle. When a small alternating current is used for input signal to the electrodes, practically all the electric charge passed during each half cycle is stored in electric double layer which acts as a capacitor. The electrodes are usually made of platinum and are platinized, that is, coated with finely divided metallic platinum. The surface area of the electrode, and hence the electrode capacitance is thereby greatly increased. The coating of the electrodes is achieved by electrolysis of a 3% solution of chloroplatinic acid containing lead acetate. In some cases platinized electrodes cannot be used because the platinum catalyzes the decomposition of the electrolyte.
Recently, an improved conductivity cell for use with solid electrolytes has been produced. This cell, which was developed by Ib Olsen of Valence Technology, Inc., Denmark, is known as a syringe-type electrolyte-conductivity cell and is illustrated in FIG. 1. This cell is disclosed in U.S. patent application No. Ser. 08/042,315, and entitled, "ELECTROCHEMICAL TEST CELL FOR TRANSPORT AND CONDUCTIVITY MEASUREMENTS" which is incorporated herein by reference in its entirety.
Such a cell comprises a plastic barrel, 3, for example, adapted from a plastic syringe by cutting off the tip of the barrel, and a pair of stainless steel rods, 4, each having at least one O-ring 5, located thereon, to contain the electrolyte, 1, and maintain contact with the electrode surface, 2.
In using such a cell, a sample of unpolymerized electrolyte (liquid) can be placed into the syringe barrel and sealed between the two electrodes. The conductivity of the liquid sample can then be measured. This sample can then be cured in situ by employing ultraviolet radiation. The curing process converts the liquid electrolyte to a solid electrolyte which is suitable for use as an electrolyte in a solid battery.
Because of the difficulty of cleaning the electrodes of the conductivity cell it would be advantageous if the cell were disposable.
In any case, the electrodes which are employed in conductivity cells (as well as conductivity probes) need a high surface area in order to provide measurements. Furthermore, the electrodes must also be inert to both the liquid and solid electrolytes, to be tested. Traditional material for use in such electrodes is a high surface area form of platinum, known as platinum black which is produced by a plating process.
While electrodes made from such materials provide the desired degree of accuracy, they are also very expensive. Accordingly, the need still exists for an electrode which is capable of providing accurate results while being more cost effective.